Rare cause of Horner's syndrome: pseudoaneurysm of right subclavian artery in an intravenous drug user.

Pseudoaneurysms of the subclavian artery are extremely rare lesions despite the overall increase in the frequency of septic pseudoaneurysms caused by illicit parenteral drug abuse. A case of subclavian artery pseudoaneurysm presenting with Horner's syndrome in an intravenous drug user is discussed.